by Tom Kenworthy
Changing water temperatures and stream flows combined with drought and increasing wildfires from global warming are creating a bleak outlook for trout in the western U.S., according to a new study.
“Despite the best intentions, we will not be able to preserve all populations of native trout in the Rocky Mountains this century,” concludes a paper that has been published in the December issue of the journal Fisheries. The study looked at five river basins in the West and was conducted by the U.S. Forest Service, U.S. Geological Survey and Colorado State University.
Though the study does not look at the economic implications of these changes, they could be large. Trout fishing is a significant part of the West’s recreational economy. According to a 2006 report by the U.S. Fish and Wildlife Service, nearly 1.6 million anglers pursue trout in the Mountain West. Nationally, trout fishermen spent $4.8 billion in 2006 — generating about $13.5 billion in economic activity, sustaining more than 109,000 jobs, and yielding more than $1.8 billion in federal, state and local tax revenues.
Numerous earlier studies have predicted big declines in trout populations under climate change; this most recent one looks at how coldwater fish habitats have already been changing in recent decades in some of the region’s most important river basins, including the Flathead in northern Montana, the Boise in Idaho, the Green in Wyoming, the Rio Grande in Colorado, and the Greater Yellowstone region of northwest Wyoming and southwest Montana.
The warming trend of recent decades — a mean increase in temperatures of .8 degrees Celsius during the 20th century — has raised stream temperatures and altered normal water flows. For fish like trout that depend on cold water, this has brought on a range of effects: less summer habitat, migrations to higher altitudes and cooler waters, greater competition with non-native species and more hybridization, and less reproduction success.
“Many [trout] populations and species will retain enough flexibility to adapt … but others are likely to be overwhelmed by future changes,” the report concludes.
Tom Kenworthy is a Senior Fellow with the Center for American Progress Action Fund.